The present invention relates to the preparation of aromatic polyesters (polyarylates) based on polar group substituted aromatic dicarboxylic acids which are used for preparing membranes having improved gas permeation properties.
This is the continuation-in-part of our U.S. patent application Ser. No. 09/181,900 filed on Oct. 29, 1998.
1. Background
Polyesters are high performance engineering plastics with good combination of thermal, mechanical and gas permeation properties. Aromatic polyesters are engineering thermoplastics prepared from aromatic diols and aromatic dicarboxylic acids. Polyarylates based on polar group substituted bisphenols have been widely investigated. However, polyarylates with polar group substituted acid moieties have been paid less attention. One of the advantage of introducing polar groups in the polymer backbone is that it increases solubility in common solvents.
Aromatic polyesters based on polar group (such as halogen atoms, nitro group, sulfo group or a similar polar group or combination of these polar groups) substituted acid can have wide range of applications. One application is their use as membrane materials for the separation of mixture of gases or liquids. Membranes made of these polyarylates have generally superior permeation properties for separations such as hydrogen from methane, helium from nitrogen, or oxygen from nitrogen.
2. Prior Art
In the prior art, aromatic polyester (polyarylates) are prepared either by one phase (solution or melt) or two phase (interfacial) polycondensation methods [G. Allen et al, eds. Comprehensive Polymer Science, 1st ed, Pergaman press, Oxford, (1989); P. W. Morgan, Condensation Polymers by Interscience, NY (1965)]. P. K. Bhowmik et al (Macromolecules 26, 5287-5287-5294, 1993) have synthesized polyarylates based on bromoterephthalic acid and biphenyls or binaphthyls in 90-95% yields and moderate intrinsic viscosities by melt condensation method. Polyarylates based on bisphenol-A, hexaflurobisphenol-A, 9,9-bis(4-hydroxy phenyl) fluorene and 3-(4-hydroxyphenyl)-1,1,3-trimethyl-5-indanol have been synthesized with tetrafluoro isophthalic acid (M. Kakimoto et al, J. Polym. Sci.: Part A: Polym. Chem., 25, 2747-2753, 1987) and with tetrafluoroterephthalic acid (Y. Oishi et al, J. Polym. Sci.: Part A: Polym. Chem., 27, 1425-1428, 1989) by interfacial and solution polymerization in good yields.
In the prior art, efforts to incorporate polar groups in the polymer have been reported in the literature for various types of polymers as typified in the following examples: Kawakami et al (Eur. Pat. Appln EP 444, 690,04 September 1991, CA: 115-257902) showed that the polyarylate based on tetrabromobisphenl-A and iso/terephthalic acid had a good oxygen selectivity over nitrogen. In an another report (Kawakami et al Eur. Pat. appln. EP 376, 234, on July 1990; CV: 114-63781) the use of tetrabromobisphenol-A and tetrachlorohexafluorobisphenol-A for making polyarylates with isophthalic acid is taught. Structural variations in other types of polymers are also reported in the literature. U.S. Pat. No. 4,840,686 (J. N. Anand et al, dated Jun. 20, 1989, CA: 112-9941) teaches the use of polycarbonate made from tetrabromobisphenol-A and iso/terephthalic acid (l/l) had permselectivity of O2 over N2 of 8.0 with O2 permeability of 1.4 barrers. In an another report (Kawakami et al Eur. Pat. appl. EP 376, 234, Jul. 4, 1990, CA: 114-63781) use of tetrabromohexafluorobisphenol-A (TBrHFbisA) and tetrachlorohexafluorobisphenol-A (TClHFbisA) for making polyarylates with isophthalic acid is taught. The polyarylate TBrHFbisA-1 had O2/N2 selectivity of 6.7 with O2 permeability of 5.25 barrers; while the polyarylate based on TClHFbisA-1 had O2/N2 selectivity of 6.1 with O2 permeability of 5.64 barrers. Polar group substituted bisphenols are also reported in other types of polymers. U.S. Pat. No. 4,840,686 (J. N. Anand et al, dated Jun. 20, 1989, CA: 112-9441) teaches the use of polycarbonate made from tetrabromobisphenol-A and phosgene. This polymer gave O2/N2 selectivity of 7.4.
Gas permeation properties of polyarylates prepared from isophthalic and terephthalic acid or the mixture of the above acids with various substituted bisphenols have been reported in the literature. Gas permeation properties of polyarylates based on isophthalic acid or t-butyl-isophthalic acid and various substituted bisphenols have been studied (M. R. Pixton and D. R. Paul, Macromolecules, 28 (1995) pp 8277-8286). The effect of halogenation of bisphenol and phenolphthalein on the gas permeation properties of iso/terephthalic acid based polyarylates has been reported (R. T. Chern and C. N. Provan, J. Membr. Sci., 59, (1991) pp 293-304). The effect of bisphenol bridge substitution on the gas permeation properties of resulting iso/terephthalates has also been reported. (A. Y. Houde et al, J. Membr. Sci., 103, (1995) pp 167-174) The effect of bisphenol ring substitution on the gas permeation properties of iso/terephthalates has been studied (U. K. Kharul and S. S. Kulkarni, Polymer, submitted).
None of the previous efforts have examined the effect of polar group substitutions on the acid moiety in polyarylates as a method of obtaining polymers with attractive gas permeation characteristics.
Preparation of aromatic polyesters based on polar group substituted aromatic dicarboxylic acid
A very few reports are found in the literature in which the nitro or bromo substituted 1,3- or 1,4-benzene dicarboxylic acid (iso or terephthalic acid) have been used for the preparation of polyesters. Preparation of liquid crystalline polyarylates based on various hydroquinones (Hq, methoxy-HQ, t-butyl-Hq, Hq-sulfonic acid) with bromo or nitro substituted terephthalic acids have been reported (Makromol. Chem. 191, 1990, pp 225-235; Macromolecules, 25, 1992, p 7107-7113). A liquid crystalline copolymer based on Br-TPA and TPA with 1, 2-benzene diol and 1,4-benzene diol has been reported (JP 07,233,249; Sep. 5, 1995; CA: 124:57077). The synthesis of polymers based on bisphenol-A with nitro-isophthalic acid or nitro-terephthalic acid have been cited in the literature (Polymer International, 29, 1992, pp 61-68; Alexandria J. Pharm. Sci. 5, 1991, pp 78-82). No transport properties for any of these polymers have been measured. None of the previous efforts have examined the effect of polar group substitutions on the acid moiety in polyarylates as a method of obtaining polymers with attractive gas permeation characteristics. In other words, no report were found on polymers prepared from polar group substituted acids with various substituted bisphenols (i.e., bisphenols having different bridge/ring substitution, substituted bisphenols containing cardo groups, bisphenols based on fluorenone).
To overcome the drawbacks associated with the prior art process, the present invention provides an improved process for the preparation of aromatic polyesters by polymerization of the bisphenol along with a suitable additive in order to obtain aromatic polyesters having high intrinsic viscosity.
Another object of present invention is to provide an improved process for the preparation of aromatic polyesters based on tetra-substituted bisphenol and polar group substituted aromatic dicarboxylic acid having high viscosity and yield.
In a further object of the present invention is to prepare aromatic polyesters (polyarylates) based on a polar group substituted aromatic dicarboxylic acids with substituted bisphenols having high gas permeability as well as selectivity.
Another object of the invention is to prepare such type of polyarylates to achieve high solubility of these polyarylates in common solvents.
Accordingly, the present invention is directed to a novel process for the preparation of a polyarylates (aromatic polyesters) with high gas permeability as well as selectivity based on polar groups substituted aromatic dicarboxylic acids with substituted disphenols.
The said process for the preparation of aromatic polyesters comprises polymerization of a aromatic dicarboxylic acid substituted with a polar group weight percentage in the range of 20 to 75 with a substituted aromatic diol weight percentage in the range of 25 to 78.
Accordingly, the present invention is directed to a novel process for the preparation of a polyarylates (aromatic polyesters) with high gas permeability as well as selectivity based on polar groups substituted aromatic dicarboxylic acids with substituted disphenols.
The said process for the preparation of aromatic polyesters comprises polymerization of an aromatic dicarboxylic acid substituted with a polar group weight percentage in the range of 20 to 75 with a substituted aromatic diol weight percentage in the range of 25 to 78 by known methods herein described.
In one embodiment, the process for the preparation of aromatic polyesters comprises the steps of (a) polymerizing a polar group substituted aromatic dicarboxylic acid having weight percentage in the range of 20 to 75, with an alkali metal salt of tetra-substituted aromatic diol having weight percentage in the range of 25 to 78 in presence of a solubilizing additive having weight percentage in the range of 2 to 20 at a temperature in the range of xe2x88x925 to 80xc2x0 C. for a period in the range of 1 to 36 hr with stirring, (b) adding the reaction mixture to a nonsolvent, (c) separating and purifying the precipitated polymer by conventional methods (d) drying the polymer at a temperature in the range of 40 to 80xc2x0 C. for a period of 24 to 48 hours to obtain pure polymer.
In another embodiment, process for the preparation of polyarylates comprises the steps of
a) dissolving the bisphenol in aqueous NaOH or KOH solution;
b) adding suitable phase transfer agent;
c) adding the acid chloride already dissolved in an organic phase under vigorous stirring for 0-4 hours;
d) precipitation of the polymer in a suitable nonsolvent;
e) drying in an oven at 40-80xc2x0 C., preferably at 50-60xc2x0 C.;
f) purification of the polymer by dissolving in a suitable solvent;
g) reprecipitation of the polymer in a suitable nonsolvent; and
h) drying in an oven at 40-80xc2x0 C., preferably at 50-60xc2x0 C., preferably in a vacuum oven, yielding the polyarylate having intrinsic viscosity of 0.3 to 1 dL/g in sym-tetrachloroethane. This polymer was then used for measurement of gas permeation properties.
In yet another embodiment, the tetra-substituted bisphenol used has the structural formula wherein R1, R2 represent alkyl groups containing
C1 to C10, CF3, phenyl, or, 
or combination of these groups and R3, R4 represent alkyl group containing C1 to C5, phenyl, F, Cl, Br, I or combination of these groups.
In a further embodiment, the tetra-substituted bisphenol has the structural formula wherein R represents alkyl group containing C1 to C5, phenyl, F, Cl, Br, or I or combination of these groups.
In yet another embodiment, the bisphenol is selected from tetramethylbisphenol-A, tetrachlorobisphenol-A, dimethylbisphenol-A, tetramethylhexafluorobisphenol-A, hexaflurobisphenol-A, tetrachlorohexafluorobisphenol-A, phenolphthalein, o-cresolphthalein, 4,4xe2x80x2-(9-fluorenylidene)bis(2,6-dimethylphenol), tetramethylphenolphthalein, tetrabromobisphenol-A, tetrabromohexafluorobisphenol-A, 4,4xe2x80x2-(9-fluorenylidene)bis-(2,6-dibromophenol), 4,4xe2x80x2(9-fluorenylidene)diphenol, 4,4xe2x80x2-(9-fluorenylidine) diphenol, 4,4xe2x80x2(9-fluorenylidene) di-o-cresol, bis(2-bromo-6-methylphenol), tetrabromophenolphthalein, dibromodimethylbisphenol-A, dibromodimethylhexafluorobisphenol-A, 4,4xe2x80x2(9-fluorenylidene)bis(2-bromo-6-methylphenol), dibromodimethylphenolphthalein and any other tetra-substituted dihydric phenols or tetra-substituted bisphenols.
In yet another embodiment, the polar group substituted aromatic dicarboxylic acid has the structural formula wherein R1, R2, R3, R4=F, Cl, Br, I or any other polar group or combination of these groups
or R1, R2, R3=F, Cl, Br, I or any other polar group or combination of these groups and, R4=H
or R1, R2=F, Cl, Br, I, or any other polar group or combination of these groups and R3 R4=H or R1=F,Cl, Br, I, NO2, SO3, H or SO3 Na or any other polar group and R2, R3, R4=H and wherein one/two/three or all four H atoms of the phenyl ring are replaced by a polar group such as halogen atom (F, Cl, Br or I), NO2, SO3H or SO3Na.
In still another embodiment, the dicarboxylic acid is selected from monobromoisophthalic acid, monobromoterephthalic acid, mono-chloroisophthalic acid, monochloroterephthalic acid, monofluoroisophthalic acid, monofluoroterephthalic acid, nitroterephthalic acid, dibromoisophthalic acid, dibromoterephthalic acid, dichloroisophthalic acid, dichloroterephthalic acid difluoroisophthalic acid, difluoroterephthalic acid, tetrabromisophthalic acid, tetrabromoterephthalic acid, tetrachloroisophthalic acid, tetrachloroterephthalic acid, tetrafluoroisphthalic acid, tetrafluoroterephthalic acid, sulfoterephthalic or any other polar group or halogen atom substituted aromatic dicarboxylic acid.
In yet another embodiment, the additive is selected from crown ether quaternary ammonium salt, tetrabutyl ammonium bromide or benzyltriethyl ammonium chloride.
In a further embodiment, the solvent for polymerization is selected from chloroform, methylene chloride, dioxane, tetrahydrofuran, nitrobenzene, dimethylformamide and dimethylacetamide and similar organic solvents.
In yet another embodiment, the nonsolvent is selected from acetone, methyl ethyl ketone, methanol, ethanol, or other simple alcohols and ketones or combinations thereof.
In another embodiment, the solvent for making polymer solution is selected from chloroform, methylene chloride, tetrachloromethane, dioxane, tetrahydrofuran, nitrobenzene, toluene, dimethylformamide, dimethylacetamide and other similar organic solvents.
In another embodiment, polymerization reaction is carried out at a temperature in the range of 40xc2x0 C. to 80xc2x0 C.
In another embodiment, the polymerization reaction is carried out at the stirring rate of 0 to 5000 rpm.
Still another embodiment, the tetrasubstituted bisphenol is dissolved in aqueous alkali metal hydroxide is preferably selected from sodium or potassium hydroxide.
Accordingly, the present invention discloses the preparation of new polyarylates (aromatic polyesters) with high gas permeability as well as selectivity which are based on polar group substituted aromatic dicarboxylic acids with substituted bisphenols. The method of preparation of these polyarylates, preparation of membranes and their gas permeation properties comprises:
Preparation of polyarylates:
These polyarylates were prepared by either solution or interfacial polycondensation of aromatic diols [substituted bisphenols, phenolphthalein, substituted phenolphthaleins, 4,4xe2x80x2-(9-fluorenylidene)diphenol, substituted 4,4xe2x80x2-(9-fluorenylidene)diphenol] with polar group substituted aromatic dicarboxylic acid chlorides. These acid chlorides were in turn prepared from their respective acids either by refluxing that acid in 4 molar equivalent of thionyl chloride for 3 to 12 hours using N,N-dimethyl formamide as a catalyst or reacting the acid with PCl5. Thus, formed acid chlorides were reacted with various dihydric phenols by usual polymerization techniques such as solution or interfacial polymerization techniques. The solution polymerization technique comprises reacting a dihydric phenol with an acid chloride using an organic base such as trialkylamine, preferably triethylamine in an organic solvent such as but not limited to chloroform, dichloromethane, tetrachloromethane, nitrobenzene or tetrahydrofuran. The interfacial polymerization technique comprises dissolving the bisphenol in aqueous NaOH or KOH solution, adding suitable phase transfer agent like tetralkyl ammonium halide or crown ether: followed by adding the acid chloride already dissolved in an organic phase such as but not limited to dichloromethane, chloroform, nitrobenzene or tetrahydrofuran under vigorous stirring for 0-4 hours. This is followed by precipitation of the polymer in a suitable nonsolvent such as but not limited to methanol or acetone and its drying in an oven at 40-80xc2x0 C., preferably at 50-60xc2x0 C. Polymer purification consists of dissolving it in a suitable solvent like chloroform, dichloromethane, tetrachloroethane or tetrahydrofuran and then reprecipitating the polymer in a suitable nonsolvent like acetone or methanol; followed by its drying in an oven at 40-80xc2x0 C., preferably at 50-60xc2x0 C., preferably in a vacuum oven, yielding the polyarylate having intrinsic viscosity of 0.3 to 1 dL/g in sym-tetrachloroethane. This polymer was then used for measurement of gas permeation properties.
Preparation of membranes:
Membrane films were prepared by solution casting which involves making 1-10% (w/w) of polymer solution in a suitable solvent such as but not limited to chloroform, methylene chloride, dioxane, tetrahydrofuran, toluene, dimethylformamide or dimethylacetamide, filtering this solution and then pouring it onto a flat glass surface, allowing the solvent to evaporate for 8-24 hours at 25-40xc2x0 C., preferably at 35xc2x0 C. in the dry atmosphere, then peeling off the formed film. Residual solvent was removed by drying these films in a vacuum oven at 50-60xc2x0 C. for a week. Gas permeabilities were measured using the variable volume method as described before (A. Y. Houde, PhD thesis, University of Poona, India, pp.82). The unit of permeability used is the Barrer which is defined as 10xe2x88x9210 cm3(STP).cm/cm2.sec.cm Hg. The selectivity is the ratio of permeabilities for two gases.
These polyarylates are easily processed into membrane form as they are soluble in common solvents such as but not limited to chloroform, methylene chloride, dioxane, tetrahydrofuran, toluene, dimethylformamide and dimethylacetamide. For gas separation applications, the solution of these polymers in the above stated solvents can be used to form hollow fiber membranes or flat sheet membranes by phase inversion or thin film composite membranes by dip coating method. Membranes made of these polyarylates have generally superior permeation properties for gas separation such as hydrogen from methane, helium from nitrogen, oxygen from nitrogen etc. In particular, the polyarylates have an excellent separation factor for various gas pairs coupled with adequately high intrinsic helium, hydrogen and oxygen permeabilities.